1. Field of the Invention
The present invention is related to a wireless communication apparatus for communicating while a plurality of frequency channels are switched, and a frequency channel selecting method. More specifically, the present invention is directed to a wireless communication apparatus and a frequency channel selecting method, capable of readily and flexibly selecting frequency channels based upon relative communication qualities.
2. Description of the Related Art
In wireless communication operations, frequency hopping techniques have been utilized, in which one frequency channel is selected from a plurality of usable frequency channels by way of a predetermined algorithm, and a channel selecting operation is repeatedly carried out at a constant time interval. There is a standard for a short range wireless communication using this frequency hopping technique, which is referred to as BLUETOOTH. The BLUETOOTH technique features low power consumption and low cost.
However, the frequency channels which are used in BLUETOOTH systems are also used in standardized wireless LAN (Local Area Network) systems, such as, for instance, IEEE 802.11b.
As a result, in conventional wireless systems, frequency channels have been selected in accordance with the following methods. That is, an error occurring rate of a packet which is transmitted is measured for each frequency channel, and a frequency channel is avoided if its packet error occurring rate exceeds a predetermined value. Also, an RSSI (Received Signal Strength Indication) is measured in each channel in order to specify a frequency channel being used in a wireless communication by another communication apparatus, and if specified, such a frequency channel is avoided based upon the measurement result. A packet error may occur when a wireless communication by one wireless communication apparatus interferes with that of another wireless communication apparatus.
However, the method for setting the threshold value with respect to the result of each of the channels in order to select such a frequency channel used in the wireless communication has the problem that the selected frequency channel is not evaluated in relation to other frequency channels. For instance, there is no problem if a sufficiently large number of frequency channels whose communication qualities are higher than the threshold value can be secured. However, there are possibly some cases, where a total number of communication apparata is increased, in which frequency channels having necessary communication qualities cannot be secured over the entire communication system. In such a difficult case, it is desirable that a frequency channel which is presently used be continuously used in order to reduce interference with respect to other wireless communications if the following conditions are satisfied. That is, even when the communication quality of the frequency channel being used is deteriorated and exceeds a present threshold value, it is evaluated that the communication quality of the presently used frequency channel is relatively better than other frequency channels.
To select a frequency channel having a relatively better communication quality, a sorting method may be conceived by which error occurring rates of selectable frequency channels and received signal strength indications are sorted. However, processing cost required for executing the sorting operation is high and power consumption consumed in this sorting process operation is also high.